There is nothing magical about ice cubes. Wool looses it's memory when wet, so you can pull dents out of the pile when it is wet.
The only reason we mention ice cube to clients is because it is a defined amount of water. If you said to a client "wet the pile" you run the risk of them pouring a bucket of water over it. (Exaggeration obviously, but you get the point.) Probably it would be more useful to say something like "no more than an egg-cup full."
Having said all that you can re-train the pile, but if the underlay is crushed you will still have some sort of dint in the carpet which will reflect light in a different way to the rest of the room.