Yes it would have been frost but I would not cut them off. In a week or twos time it will get warm and sunny again (?????) the brown tops will go brittle and you can then just rub them off. Better luck next year.

I agree with Bulba..just leave them..mine are the same..In the first instance it is the frost,but if they get early morning sun,while they are still wet,that does most damage..in a shaded place the frost would just melt and dry naturally..not a lot we can do really,