A week ago, someone had some problems with DBMS_XMLSCHEMA.PURGESCHEMA (available in Oracle 11g). In principle, the problem he had, was that a registered schema could not be deleted via the normal procedures/methods, or at least this was claimed to be the case…
The problem was solved via a very intuitive way (direct delete via a user view), but one I wouldn’t recommend PLUS it also raises some questions…(although I am still not sure how under what circumstances this was doable / which privileges used to make this happen)…
Have a look at the following OTN Forum post, regarding “Purgeschema“. A description of the view user_xml_schemas is shown below as a reference.