If it were me, I would use a tiny amount of gentle soap, I.e. Dreft, or fairy hand wash etc on a sponge and just give that a go. My sofas have been through the mill, believe me, and are now about 12 years old, and it was only me going at them with huge amounts of energy( not a common thing) which ruined them! I have removed numerous marks from them. They really are quite resilient.