How to clean off old elastomeric

We have a flat roof that sprung a leak last year, I’m just getting around to repairing it. What I found is that the existing elastomeric coating was not put in correctly – it is bubbling (meaning the elastomeric has air underneath it) to the point where I can peel it off, and when I do that, I find a lot of dirt between that layer and the underneath layer.

I want to apply Henry’s tropicool (the silicone version) over the area instead of another coat of elastomeric, but I want to ensure I clean it properly. Where it bubbles, I pressure washed it to get most of it loose, then removed it by hand till I don’t see anymore dirt. But still, there are a lot of loose pieces dangling around the edges where I peeled.

Before I roll on the Tropicool, is there anything else I can or should do to get it super clean/prepped? I don’t want to have more bubbles/boils next year, although I can say for sure there will be close to no dirt between the roof and coating I am about to put on.