I like to look at caching as a form of denormalization - introducing redundancy to improve performance. And whenever we have redundancy, we have to make sure all our copies are synchronized, which can be tricky, especially in a concurrent environment.

On the other hand, the whole point of normalization in databases is to avoid redundancy and have "single source of truth".

I find the concepts of normalization and denormalization applicable and helpful outside databases as well, though a different terminology is often used.