It would be really nice to have this not have to touch every actor in the game. The way I'd do it is add a `generation` number to the actor, and have a Target invalidate itself if the generation number doesn't match what it was when the actor was set up.

If you have a look at the implementation of Target, you'll see we already do a similar thing for low-overhead handling of ownership changes, which would otherwise require broadcasting an event to everything.