I agree with washing in Synthrapol. It may take several washings to get all of the bleeds out.
Synthrapol requires hot water, but I would not agitate. If you do it in a top-loading washing machine, stop the machine so it does not agitate and simply press down with your hands to agitate (wearing rubber gloves to protect your hands from the hot water!). Spin, add rinse water, stop machine agitation and do manual agitation, spin out the rinse water, and take a look at the quilt. You can also do this in a large sink or a bathtub. Just be aware that you want a *lot* of water for the loose dye particles to stay suspended in.