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Once the card leaves play it is no longer being tartgeted. When it enters play again it has reset and is not longer the same target (even if it's the same card).
The artifact pile is still in play, so even though you can't normally target face-down Artifacts because of targeting restrictions on face-down cards, the active Art never leaves play to reset with Urim.
Face Down cards are cards in territories, battle, and set-aside areas that are face down either due to special ability, or are inactive artifacts in an artifact pile. Face down cards have no abilities, brigade, titles, or identifiers while they are face down. The only known attribute of a face down card is the card type. Face down cards are only targetable by abilities that specify they can target face down cards or inactive artifacts, or cards that can target any or all cards in a location. When a face down card enters battle, it is immediately flipped face up, unless otherwise specified by the special ability that flipped it face down.
And?
In play is not an untargetable location and face-down is not a location.