MESI cache coherency

RU: MESI cache coherency

A cache coherency protocol used in multi-core CPUs to keep private L1/L2 caches consistent. Each cache line is labelled with one of four states: Modified (dirty, owned by this core), Exclusive (clean copy, only this core holds it), Shared (clean, multiple cores hold copies), or Invalid (line must not be used). When a core writes to a Shared line, it broadcasts an invalidation so other cores mark their copies Invalid before the write proceeds.