Perhaps the advantage of this method over Jefromi's answer is that you don't have to remember which behaviour of git reset is the right one :)
# Create a branch to throw away, on which we'll do the cherry-pick:
git checkout -b to-discard
# Do the cherry-pick:
git cherry-pick stuff
# Switch back to the branch you were previously on:
git checkout -
# Update the working tree and the index with the versions of A and B
# from the to-discard branch:
git checkout to-discard -- A B
# Commit those changes:
git commit -m "Cherry-picked changes to A and B from [stuff]"
# Delete the temporary branch:
git branch -D to-discard