on erasing the ``racket repl'' buffer created by geiser

[Wayne Harris]

Here's my Racket REPL's buffer.

--8<---------------cut here---------------start------------->8---
Welcome to Racket v7.6.
racket@> ,enter "c:/tmp/api.rkt"
racket@api.rkt> (+ 1)
1
racket@api.rkt> (+ 1 3)
4
racket@api.rkt> (+ 1 3 5)
9
racket@api.rkt>
--8<---------------cut here---------------end--------------->8---

If now I select any part of this buffer and try to kill it (say with
kill-region), I can't.  I get the message

  kill-region: Text is read-only: #<buffer * Racket REPL *>

How can I get clear up the entire buffer, or at least kill a region?
Thank you!