diff --git a/hal/stm32f4.c b/hal/stm32f4.c
index 78084936..96082ffb 100644
--- a/hal/stm32f4.c
+++ b/hal/stm32f4.c
@@ -196,9 +196,35 @@ void RAMFUNCTION hal_flash_unlock(void)
     FLASH_KEYR = FLASH_KEY2;
 }
 
+/* RM0090 3.5.1: the instruction and data caches keep lines fetched before an
+ * erase/program, so a read-back through the flash memory map can return
+ * pre-erase bytes. The reset bits are only writable while the corresponding
+ * cache is disabled, hence the disable/reset/re-enable dance. */
+void RAMFUNCTION hal_cache_invalidate(void)
+{
+    uint32_t acr = FLASH_ACR;
+
+    if (acr & FLASH_ACR_ENABLE_INST_CACHE) {
+        FLASH_ACR &= ~FLASH_ACR_ENABLE_INST_CACHE;
+        FLASH_ACR |= FLASH_ACR_RESET_INST_CACHE;
+        FLASH_ACR &= ~FLASH_ACR_RESET_INST_CACHE;
+        FLASH_ACR |= FLASH_ACR_ENABLE_INST_CACHE;
+    }
+    if (acr & FLASH_ACR_ENABLE_DATA_CACHE) {
+        FLASH_ACR &= ~FLASH_ACR_ENABLE_DATA_CACHE;
+        FLASH_ACR |= FLASH_ACR_RESET_DATA_CACHE;
+        FLASH_ACR &= ~FLASH_ACR_RESET_DATA_CACHE;
+        FLASH_ACR |= FLASH_ACR_ENABLE_DATA_CACHE;
+    }
+}
+
 void RAMFUNCTION hal_flash_lock(void)
 {
     FLASH_CR |= FLASH_CR_LOCK;
+    /* Drop the stale cache lines at the end of the write/erase batch: every
+     * sequence in wolfBoot ends with a lock, so one invalidate per batch
+     * covers every consumer that reads flash back. */
+    hal_cache_invalidate();
 }
 
 
diff --git a/hal/stm32g4.c b/hal/stm32g4.c
index 08c994b6..137f1436 100644
--- a/hal/stm32g4.c
+++ b/hal/stm32g4.c
@@ -98,11 +98,37 @@ void RAMFUNCTION hal_flash_unlock(void)
     }
 }
 
+/* RM0440 3.3.3: the instruction and data caches keep lines fetched before an
+ * erase/program, so a read-back through the flash memory map can return
+ * pre-erase bytes. The reset bits are only writable while the corresponding
+ * cache is disabled, hence the disable/reset/re-enable dance. */
+void RAMFUNCTION hal_cache_invalidate(void)
+{
+    uint32_t acr = FLASH_ACR;
+
+    if (acr & FLASH_ACR_ICEN) {
+        FLASH_ACR &= ~FLASH_ACR_ICEN;
+        FLASH_ACR |= FLASH_ACR_ICRST;
+        FLASH_ACR &= ~FLASH_ACR_ICRST;
+        FLASH_ACR |= FLASH_ACR_ICEN;
+    }
+    if (acr & FLASH_ACR_DCEN) {
+        FLASH_ACR &= ~FLASH_ACR_DCEN;
+        FLASH_ACR |= FLASH_ACR_DCRST;
+        FLASH_ACR &= ~FLASH_ACR_DCRST;
+        FLASH_ACR |= FLASH_ACR_DCEN;
+    }
+}
+
 void RAMFUNCTION hal_flash_lock(void)
 {
     flash_wait_complete();
     if ((FLASH_CR & FLASH_CR_LOCK) == 0)
         FLASH_CR |= FLASH_CR_LOCK;
+    /* Drop the stale cache lines at the end of the write/erase batch: every
+     * sequence in wolfBoot ends with a lock, so one invalidate per batch
+     * covers every consumer that reads flash back. */
+    hal_cache_invalidate();
 }
 
 
diff --git a/hal/stm32g4.h b/hal/stm32g4.h
index 2cec5a8c..2c2e46ba 100644
--- a/hal/stm32g4.h
+++ b/hal/stm32g4.h
@@ -102,6 +102,8 @@
 #define FLASH_ACR_PRFTEN          (1 << 8)
 #define FLASH_ACR_ICEN            (1 << 9)
 #define FLASH_ACR_DCEN            (1 << 10)
+#define FLASH_ACR_ICRST           (1 << 11)
+#define FLASH_ACR_DCRST           (1 << 12)
 #define FLASH_ACR_LATENCY_4WS     (0x4)
 
 /* G4 has a single BSY at bit 16 (no BSY1/BSY2 like G0). */
diff --git a/src/libwolfboot.c b/src/libwolfboot.c
index dca3f523..5569d645 100644
--- a/src/libwolfboot.c
+++ b/src/libwolfboot.c
@@ -244,6 +244,14 @@ static const uint32_t wolfboot_magic_trail = WOLFBOOT_MAGIC_TRAIL;
 #define FLAGS_UPDATE_EXT() PARTN_IS_EXT(PART_UPDATE)
 #endif
 
+/* Weak no-op default: targets whose flash reads are not cached need not
+ * implement this. It lives outside NVM_FLASH_WRITEONCE because callers such
+ * as src/pkcs11_store.c are built independently of that option. */
+void WEAKFUNCTION hal_cache_invalidate(void)
+{
+    /* if cache flushing is required implement in hal */
+}
+
 #ifdef NVM_FLASH_WRITEONCE
 /* Some internal FLASH memory models don't allow
  * multiple writes after erase in the same page/area.
@@ -282,10 +290,6 @@ static uint8_t get_base_offset(uint8_t *base, uintptr_t off)
     return *(uint8_t*)((uintptr_t)base - off); /* ignore array bounds error */
 }
 
-void WEAKFUNCTION hal_cache_invalidate(void)
-{
-    /* if cache flushing is required implement in hal */
-}
 #ifdef __CCRX__
 #pragma section FRAM
 #endif