cache, as well. The mini-data cache is 2-way, so src and dst won't
clobber each other, and the smallness of the cache doesn't matter,
since we access each page once sequentially.
While we still have to do the initial clean of the source page, this
saves another 4K of main D$ pollution, and also means we don't have
to do 2 cache passes after the copy is complete (i.e. we can skip the
invalidation of the source page in the main cache, since it's no longer
there).
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