Do you use an ACV rinse? My way of making sure I get a squeaky clean scalp is to submerge my head in a dilute ACV solution and give myself a nice massage. My head feels oh so good afterwards. Even better after conditioning with UBH conditioner.
The peppermint in the UBH gives my scalp that "just brushed" feeling...(or is that a line with re: to teeth.
) Alternatively, you can do an overnight treatment by making a concoction of penetrating oils (eg jojoba, emu, avocado or coconut with a few drops of peppermint or rosemary essential oils) applying it to your hair or scalp and sleeping in a plastic cap. Then in the morning, don't shampoo, but just do an ACV rinse, head submerged again for a good scalp massage. Concentrate on your scalp not your hair; use your fingertips not your nails. The cooler the water the better. Your hair should look nice and shiny afterwards and your scalp should feel oh so good. I usually follow this with a serum, but you can apply your choice of leave-ins on your wet hair. I like oils coz they enhance the shine.
If you still find you have gunk on your scalp, you might wanna try using castille soap for your scalp only (don't worry if it goes into your hair but the focus is to clean the scalp) and then concentrate your moisturizing/detangling/conditioning shampoo and conditioner on just your hair not your scalp. End this wash with an ACV rinse and you should feel your scalp go "aaah!"
HTH