Explain the concept of cache coherence in multi-core CPU design.

Cache coherence refers to the consistency of data stored in different caches within a multi-core CPU design. In a multi-core system, each core has its own cache memory to store frequently accessed data. However, when multiple cores are accessing and modifying the same data, it can lead to inconsistencies and errors.

To ensure cache coherence, protocols like MESI (Modified, Exclusive, Shared, Invalid) are used. These protocols maintain a directory or a table that keeps track of the status of each cache line. When a core wants to read or write to a cache line, it checks the directory to determine if the data is already present in another cache and if it is valid or modified.

If the data is present in another cache and is marked as modified, the cache requesting the data must first invalidate or update the other cache's copy to ensure consistency. This process is known as cache coherence protocol.

Cache coherence ensures that all cores see a consistent view of memory and prevents data races, where multiple cores try to modify the same data simultaneously. It also helps in maintaining data integrity and avoiding inconsistencies that can arise due to caching.