Most likely the bark was damaged during the winter from the cold, and that's why wood lice are able to inhabit it. Your cordyline may not recover fully, or at all, and there's nothing you can do to help it - it may produce new growth from the base though.

Mine done this last year, then it produced lots of new growth from the base as Bamboo says. Unfortunately this last winter it died.
So I am growing sweet peas up it and I shall rip it out in the winter. This gives me chance of buying and trying something different.