Just for confirmation,
if I attack a zone with a "Blood Dragon Knight":
"Action: When this unit attacks, deal damage equal to its power to target unit in the defending zone."
and my opponent have in the defending zone a Hero with attached: "Shield of Aeons":
"Order only. Attach to a target Hero or legend. This card cannot be targeted by card effects. While attached Hero or legend is participating in combat, cancel all damage assigned to it."
If I play the action of the "Blood Dragon Knight", and I target the Hero, the damage, is not cancelling by the "Shield of Aeons", because the Hero at the moment is not participating to the combat, correct?