Scrubbing logic in a local coherency domain issues to at least one cache
hierarchy in a remote coherency domain a domain reset request that forces
invalidation of any cached copy of a target memory block then held in
said remote coherency domain. A coherency response to said domain reset
request is received. In response to said coherency response indicating
that said target memory block is not cached in said remote coherency
domain, a domain indication of said local coherency domain is updated to
indicate that said target memory block is cached, if at all, only within
said local coherency domain.