Cache coherence protocols are essential in multiprocessor systems to ensure that multiple caches maintain a consistent view of shared data. When different processors have their own caches, changes made to a shared variable in one cache must be reflected in others to prevent inconsistencies. These protocols help manage how data is read and written across caches. There are several types of cache coherence protocols, including MESI (Modified, Exclusive, Shared, Invalid) and MOESI (Modified, Owner, Exclusive, Shared, Invalid). Each protocol has its own rules for managing data states and communication between caches, ensuring that all processors see the same data at any given time.