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Cache coherency

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 (and is mimicked in distributed shared memory systems) in which each CPU has a non-shared cache of a shared memory area. Cache coherence is special case of memory coherence.

Various protocols have been devised for maintaining cache coherency, such as the MESI protocol, MSI protocol, MOSI protocol and the MOESI protocol. Most of the cache protocols in multiprocessors are supporting sequential consistency model.

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