Beyerdynamic velour earpads can be tossed in the washing machine with your linnens and benefit from liquid fabric softener. I've laundered the pads on my dt-770's four times that way.
AKG fabric earpads are probably also durable enough for the washing machine, but pleather earpads generally are not up to the abuse. This is one of the many reasons why i hate pleather earpads. They get greasy and there is nothing you can do to get them really clean. AKG K3/4/50x pleather earpads are torn to shreds by a washing machine.
A friend tells me that Sony MDR-V600 pleather earpads can survive the gentle cycle but they will lose the foam on the back of the fabric that covers the drivers. Not that anyone here seriously uses the V600's. V6's have real leather, iirc, at least the old ones did.
I tend to buy used and even very old headphones, which are sometimes filthy. I use a small brush to clean out dirty vents, and I find that armor-all "cleaner wipes" do a good job of cleaning up grungy plastic. And yes, they do impart a small amount of armor-all, which doesn't hurt at all.
I do sometimes wipe them down with alcohol, owner's manual recommendations be damned. But again, I'm talking about 20 year old headphones that were rescued from the dog's bed and vacuumed off before listing on ebay.
But for headphones that aren't very dirty, a damp cloth really ought to do the job.