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I understand that MESI is a subset of the MOESI cache coherency protocol. But what does the Owned state in the MOESI protocol represent? What are the differences in state transition due to the extra Owned state in MOESI as compared to MESI?

For example consider same cache line in processor P1 is in OWNED state & processor P2 is in SHARED state. What happens when there is a write request to P2?

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Owned state indicates that the data is shared between multiple caches/memory levels and is modified(by the owner) unlike modified state which indicates that only this cache has the only valid value and has modified the value. This eliminates the need for writing back to the main memory before sharing the data with anyone. Hope that helps.

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