Thought I'd throw in my 2 cents as well!
Does his food have any corn in it? Because I've heard this can make them itch. Also my vet sells a spray especially for dry skin. I forget the name, I will have to look later, if you want it. Anyways..it might help! Lucky was scratching alot, too, so we changed his food from Nutro(which has corn) to Wellness, and his scratching has subsided alot!