Answer: What you describe sounds like either scale or mealybugs, either of which are more likely to attack plants which are under stress (such as the frost damage you report). These are difficult to control on large shrubs and the usual thing to do is to wait until natural predators arrive to lower the population. There are a number of parasitic wasps that feed on mealybugs and scale insects so you may not need to do anything to control the pests. If you decide you want to spray to control them, you can use insecticidal soap.
Best wishes with your hollies!
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