In a nutshell: First it says it's a construct of the human mind, like Crinos form in werewolf causes people to forget. I think this has the most internal consistency -- because the Mists vary by Banality, which is logical; the less Banal, the less your mind rebels against the idea of the chaos that is Glamour. But because it would then be literally a roadblock within the Mage's own mind, Mind Magick (and possibly Spirit) would affect remembrance. OTOH, other places make it sound like the Dreaming is a sentient omniscient entity that somehow senses a breach, measures someone's Banality, and then takes a deliberate action. This makes a lot less sense to ME. (Cleared Mists in the former case would be -- somehow that Fae hasn't the same shocking effect on the human mind as most. In the latter instance, the Dreaming really hates your damn guts for some inexplicable reason.)