Yes — bouncing a creature to its owner's hand removes all damage marked on it. This happens because when a permanent leaves the battlefield, it ceases to exist as a game object on the battlefield. When it returns to a different zone (the hand), it is treated as an entirely new object with no connection to its previous existence.
The key rule is CR 704.5c, which states that a creature with toughness greater than 0 that has damage marked on it equal to or greater than its toughness is destroyed. However, this state-based action only applies while the creature is on the battlefield. Once it moves to the hand, damage is no longer tracked on it at all, per CR 119.6, which specifies that damage marked on a permanent is removed when it leaves the battlefield.
Additionally, CR 400.7 establishes that an object in a new zone is a new object with no memory of or connection to its previous existence, meaning any history of damage, counters, or other effects from its time on the battlefield do not carry over.
Concrete example: Your opponent's 2/2 creature has already been dealt 1 damage this turn. You cast Unsummon, bouncing it to their hand. When they replay that creature next turn, it enters as a fresh 2/2 with zero damage marked on it — it would take a full 2 damage to put it at lethal again.
This also means that bouncing is an effective way to save your own creature from lethal damage mid-combat, as long as the bounce resolves before state-based actions destroy it (i.e., before it accumulates damage equal to its toughness).
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.