With freeze damaged shrubs like ixoras and crotons we would suggest waiting until freeze danger is past (end of February) to do any pruning. At that time the dead wood can be pruned back to living wood. To determine where the wood is alive, scratch the bark of a shoot near the tip to expose the cambium layer. This is the layer of tissue that lies just under the bark. Where the cambium is green the wood is alive. Where it is brown or black the wood is dead. One can also simply wait until new growth emerges and then prune back to the new growth

If your ixoras and crotons are well established they will likely eventually come back, even if they are frozen nearly to the ground.