Book Problems Culler and Singh:

The Sun Enterprise 5000 does not use a upgrade transaction, for some of the reasons that we have discussed.  However, it does avoid transfering data on a BusRdX transaction if it turns out that the issuing cache is the only one that has the data.  The idea is a simple extension of the way that memory is waved off on a BusRd when one of the caches has the block in M.  Use our three wired-OR signals for reporting status of relevant blocks.  Can you get the desired behavior.  (Hint: the issuing cache snoops its own tags during the transaction.)