It isn't enough to just shampoo your baby's delicate scalp. You also need to help him or her get rid of the flakes.
Think of the rubdown as a very gentle exfoliation. Baby hair brushes have soft, natural bristles that, to an adult, feel like barely anything at all. There are several hair tools marketed as "cradle cap brushes," but there isn't much of a difference, if any.
Just like you'll want to be shampooing more frequently, you should also be brushing more frequently. Gently massage the baby's scalp and use the brush while shampooing to help remove scales. (If you pick at them, you can irritate the skin, which can lead to infection.)
Another option, if you don't have a brush handy or your baby isn't fond of it, is to use a terrycloth towel. (Following up the whole process by swaddling your infant in an adorable hooded robe is optional.)