Been out for a while and just saw this. Mpowers is correct - no water, no heat. By now I suspect it's dry anyway. You can use a soft brush to brush off the white chalk marks. You have to be careful if it's a woven
velour (Magic, Memorable, Marvel, Majestic,
etc) If you brush too vigorously the little tufts will come out. This is especially true if the fabric is damp.
The white chalk looking stuff is the flame retardant salts. In all likelihood the drape will not pass an
NFPA 705 test if there is much residue or if it got completely saturated. All the same, I'd perform one as soon as it's good and dry. You may get lucky. If you need help with the
NFPA 705 procedure feel free to PM me or give me a
call.
If it fails the 705 about all you can do is replace it. It can be professionally cleaned and retreated. There are several companies that offer this service - Us, Reynolds Drapery in New York, I think there's another in Chicago and folks here can probably name more. Typically refurbishment costs run about 50% - 75% of replacement by the time the extra packing and shipping is calculated. They also shrink when cleaned; sometimes a lot. If the drape is showing signs of dry rot or deterioration, if the pile is loose anywhere, or it won't work at 3% - 5% smaller, cleaning probably isn't an option.
In my opinion cleaning & retreating cotton
drapes is generally not a good value anyway. In cases of super ornate
curtains it sometimes makes sense. Occasionally I run into
curtains with some sentimental/historical significance and that kind-of makes sense. But most of the time it's just better to put the cost towards a new synthetic curtain and be done with it.
The spry on flame treatments don't work very well. If you spray it on heavy enough to work, the drape will be covered with white chalky residue - the FR salts. No salts, no FR treatment.
Hope there is something of use in my ramblings. Good luck.