dm-merge is a simple tool to apply changes recorded in a copy-on-write exception table. It can be effectively used to either "commit" the changes into the source (as made with simple snapshot target) or "rollback" (reverting to a state the snapshot was created; as made with snapshot linked to snapshot-origin target). And while LVM snapshots are simply (maybe not so simply, actually) the latter case, it can revert a logical volume to the exact state it was when the snapshot was taken.