I bought two 6" miniature schefflera that turned out to have scale. I tried to crush all of the scale I could find and washed the plants in detail with soapy water on a cotton swab. I managed to get rid of scale on one of them, after doing that for weeks.
I had to throw the other away.
If I had scale again, I'd probably try a houseplant insecticide that says it kills scale, like Bonide Eight:
https://smile.amazon.com/AMES-Companies-Inc-110-12-Ounce/dp/B002LFGHXG/