I don't have KiwiGrip, but I've got something very similar that I did using two part poly paint
and fumed silica. It looks like KiwiGrip, though.
I find the only way to get it clean is to use lots of soap (simple green) and scrub, scrub, scrub! On your hands and knees if possible using a short, fine, nylon bristle scrub brush.
Some background; I did the boat in two stages; the cabin
top first, then the side decks. When I did the cabin
top I didn't go over and over the paint with the loop roller (like the KiwiGrip instructions tell you to). I just applied the paint using a notched trowel and went over it with a loop roller once or twice. The result was high spikes but a less-then-even finish. When I did the side decks I went back and forth over the paint until the finish was even. The thing is, now it's the side decks that hold onto dirt like mad. There seems to be many small cavities in the finish that the dirt can get stuck in. The top decks clean much more easily. So, this may be something to think about for those of you looking at KiwiGrip.
Here's a link to how my deck turned out, with a close-up of the finished texture.