cache-coherence MOESI protocol

Question

processor A owns a cache line which is shared with processor B.
what happens when B tries to write to that line?
also, if it was 'invalid' instead of 'shared' would it make any difference?
thank you.

Answer 1

I found this:
"If a processor wishes to write to an Owned cache line, it must notify the other processors that are sharing that cache line. Depending on the implementation it may simply tell them to invalidate their copies (moving its own copy to the Modified state), or it may tell them to update their copies with the new contents (leaving its own copy in the Owned state)."