An alternative scheme is the shared cache organization in which, rather than associating caches with processors, a cache is associated with one or more memory modules such that all processors can reference the cache. Picture shows the structure of a shared cache-based multiprocessor where a cache is associated with each set or cluster of memory modules. Thus, when a processor updates cache i, coherence is maintained by a write-through to the relevant memory In module i. No other copies of the same data reside in any of the other caches.