Many multiprocessors distinguish between a cache block that is really shared and one that exists in the clean state in exactly one cache. The addition of a "clean and private" state eliminates the need to generate a bus transaction on a write to such a block. Another enhancement in wide use allows other caches to supply data on a miss to a shared block.
1) Justify the following statement: "The addition of a "clean and private" state eliminates the need to generate a bus transaction on a write to such a block."
2) How to implement the cache protocol to support a "clean and private" state?