If you have a powerful magnet lying around (I use a rare earth one pulled out of some piece of junked machinery) you can try "swirling" it around the disk a few times. I've been doing this to used 1.44mb disks that I'm formatting to 400/800k for my Mac 512k and Apple IIgs; I find the disks almost always fail to format with the PC format present, because the write head current of the lower density drives can't overwrite it, but doing the scrambling thing with the magnet lets them work about 80-90% of the time.

(I'm totally aware it's not really kosher to use the HD disks for DD formats, but I'm just using them to slap games and such on so it's not a major tragedy if one fails; just need to reimage it.)