How do I wash my hair if I have shingles (herpes zoster) extending deep into my hairline?

Gently. Washing hair on one's scalp where there is shingles is the same as washing normal hair . . . Except that one must be gentle and not scratch the scalp lesions and scabs with his fingernails. Allowing the scabs to heal and come off the scalp by themselves is the best thing to do. Once dead skin and scabs are off the skin and just on the hairs, they can be removed by sliding them off the hairs.
Shingles. The lesions spread through nerve fibers. Thus, washing your hair will not spread it. Use a spray in your hair with your head leaning backward to prevent drainage into your eyes. Do not scrub or agitate the area.