What is Memory Mapping in Cache?
Memory mapping is the (complex) process that associates an address value (usually a 32 or 64 bits number) to some existing physical location in the hardware. This location can be in RAM, in a cache of some level, or even on the hard disk ! During program execution, data can move from one location to another, and possibly be duplicated.

The system keeps track of that and makes the mapping transparent so that the program can keep using the same address. Things get tricky when the values are modified and coherence between the copies must be guaranteed.