Posting on the community forum is usually enough - if there's no risk involved in removing the entry, the boulder team will typically amend the list within a week or two. No guarantees, though.
The list itself is not public; this was discussed a while back. However, if you get the "policy forbids issuing" error, that's definitely a blacklisted domain, so one way to know is to attempt to validate ownership for your domain. Perhaps it would make sense to create a documentation page for this and reference it in the error message.