Many people wash their hair too frequently and use harsh shampoos, drying heat and styling products. All of this dries the scalp and makes it feel itchy. Jason's Organic Tea Tree Oil Shampoo (you can find it at drugstore.com or most beauty supply stores) normalizes the scalp and gets rid of dry, itchy scalp.
Don't shampoo your hair every day or even every other day. Wait several days between shampoos--a week if your hair isn't the super oily type. (This may seem like a contradiction to say you can have dry scalp and oily hair simultaneously, but not so!)
Gently massage the tea tree oil shampoo into your scalp. Rinse thoroughly with cool water. Try to avoid heat for a while and air-dry your hair instead. Don't load it down with styling products that contain alcohol. If you can go without hair spray (same reason--nearly all hair sprays contain alcohol), do so. If not, use only a very tiny spritz.
With this regimen, your hair should feel soft and healthy, and your dry itchy scalp should be a thing of the past.