If twig ends snap when bent, at least the end of the twigs is dead.  If there are no leaves anywhere along the twigs, that entire twig may be dead.

Check to see if twigs are normal color - red-orange to green.   If they are grey, brown or black they may be dead. 

Red-twig dogwoods are not drought-tolerant shrubs.  Did they get any water during the winter?  Are they in a hot dry location?  

The roots are probably still alive, so you can, as a last resort, prune back all twigs to 2 inch stubs, just above ground.  Mulch the planting and rooting area with wood chips or similar, no more than about 2" deep.  Water the mulch and rooting area.  You may see in a few weeks some new shoots come up from the roots.