On another thread like this just a few weeks ago someone mentioned using a Magic Eraser--Mr Clean---. I had the same problem with little bits of fusible on my iron (even with using a teflon applique mat!). Just happened to have a brand new Magic Eraser.....and it worked!!! VERY well!!!
I also have some 'paste' for cleaning an iron (very hot iron, put paste on old towel and run iron back and forth til clean) but the Eraser is soooo much easier and less 'involved'!!!!