Ok, but then what does the dev do if it fails?

It sounds like you want to use the cache as a private local memory near the core, this is called a scratchpad memory. And to maintain the scratchpad memory a DMA is usually used.

It is much more reliable than a cache that can evict data behind your back. Because we generally have no (or little) control over the cache eviction policy, and an interrupt or context switch can evict what you purposely fetch in the cache (and cache coherence can also cause data eviction).

PS: Note that in some circuits the scratchpad and the L1 cache share the same memory, this enables an adjustable cache and scratchpad size