The Data Cache for Cortex-M7 devices is currently disables, due to a lack of in-depth understanding of cache policies during porting. The Instruction Cache however is enabled, since it only gets read.

See:https://github.com/modm-io/modm/blob/develop/src/modm/platform/core/cortex/startup.c.in#L95-L98

In addition to enabling the cache, the caches must be invalidated manually on certain operations (writing Flash for example).
This is however not just an issue on Cortex-M7, since most Cortex-M devices have some sort of vendor specific cache implementation for their Flash reads, which must also be manually invalided.

cc@mikewolfram