Cache Coherency refers to the consistency of data stored in multiple caches within a computer system. When multiple processors access shared data, they may store copies in their local caches. If one processor updates its copy, the other caches must reflect this change to prevent inconsistencies. To maintain Cache Coherency, systems use protocols that ensure all caches have the most recent data. These protocols can be categorized into two main types: write-invalidate and write-update. By managing how data is shared and updated, cache coherency helps improve performance while ensuring data accuracy across the system.