1. Create the structure of the global temporary table once, outside of pl/sql.
2. Utilize that table in your procedures. The contents of the table will be local to your session and will automatically disappear when you either log out or commit, depending on how the table is configured.

Multiple sessions can use the same GTT at the same time, but they will not be able to see or interact with each others data. They will also not block each other for any action against that table.