Cache coherency (alternatively
cache coherence or
cache consistency) is the property that accessing a
cache gives the same value as the underlying data, even when the data was modified by a different process after the caching was performed. This is important for consistent operation of
multiprocessor systems in which each
CPU has a non-shared cache of a shared
memory area. Various protocols have been devised for maintaining cache coherency, such as the
MESI protocol[?] and the
MOESI protocol[?].