Its very difficult to get a full scholarship at Harvard, but they do offer generous scholarships. They offer assistance by way of loans and fellowships  But as reported, nearly half their class gets a scholarship of around $33,000. You need to demonstrate need so they give need-based assistance.

You can always email their financial support office and inquire if they accept any particular external scholarships ( if you have one that is )

I hope my answer helps. All the very best for your future endeavors!