Check the trunks from top to bottom for signs of rotting, with or without white or orange gunk oozing out. If they're okay, then just wait - probably the growing points at the top have been destroyed by the cold, but you may find new growth popping out lower down the trunks, or from the base, or both. When that appears, saw the trunk down to where the growth is. If you have some evidence of rot on the trunks, but no orangey stuff pouring out, just wait and see how it goes - if it gets worse, you'll need to cut back beyond the rotted point, and if there's orangey stuff coming out, cut down beyond it now. And then wait to see if new growth arrives somewhere - you may have to wait till June.