Cache coherence refers to the consistency of data stored in multiple caches within a computer system. When multiple processors access shared data, each may store a copy in its own cache. If one processor updates its copy, the other caches must reflect this change to prevent discrepancies, ensuring that all processors see the same data. To maintain cache coherence, various protocols are used, such as the MESI protocol, which stands for Modified, Exclusive, Shared, and Invalid states. These protocols help manage how caches communicate and update each other, ensuring that all processors operate with the most current and accurate data.