Help! Viburnum Tinus tree problems

Hi - we have several Viburnum Tinus Lucidum in tree form. After the March/Easter cold spell they all lost their leaves and don't look great. No sign of new buds as yet. Can anyone advise - will they make a comeback, do we need to prune them to encourage some new growth? Any help from those knowledgeable about Viburnums greatly appreciated.