You need to use game attributes for this.
If you don't want to set up individual game attributes for something like this, you might want to consider automating it by using a Map game attribute, and coming up with some way to uniquely identify each actor that you want to track. Then you can set the unique key to true/false depending on whether the treasure has been collected.
For example, you could use scene name + actor x position + actor y position as they keys for your map. Then, as long as you don't rename the scene or move your actor, the key won't change, and when you load your game next time, the treasure will still be removed from the scene. And you can place that code in a single behavior that will work for all actors its attached to.
That's just an example. Perhaps there's a better solution for you, but it depends on how your game works.
