Equipping a champ with 9-piece Mercurial, I was surprised to notice that Fabian's A3 will still trigger the "cooldown increased" effect while Total Guard blocks its damage.

Total Guard effect clearly states:

"Each stack blocks all incoming damage and any associated effects."

I see no way to read this so that Fabian's A3 (which deals damage) would still increase skills' cooldown (which happens after the damage part of the effect), so this is a clear bug of some kind. I assume, though haven't tested, that it applies to all attacks that increase skill cooldown.