In memory hierarchical, it needs to be coherence and consistency. However, they are different things. What are the differences?
Memory coherence: a memory system is coherent if any read of a data item returns the most recently written value of that data item (what values can be returned by a read).
Memory consistency: A memory consistency model for a shared address space specifies constraints on the order in which memory operations must appear to be performed (i.e. to become visible to the processors) with respect to one another.(when a written value will be returned/seen by a read).
Coherence defines the behavior of reads and writes to the same memory location, while consistency defines the behavior of reads and writes with respect to accesses to other locations.