How to release space

From: bob123 <bob123_at_gmail.com>
Date: Mon, 18 Jan 2010 21:17:10 +0100
Message-ID: <4b54c1c3$0$12223$426a74cc_at_news.free.fr>

I have a big table with 2 clob columns
I have to truncate this table

I did:
> truncate table blabla reuse storage;

after I did:
> alter table blabla deallocate unused;

but it doesn't free space allocated for the LOBSEGMENT's how can I get the released space ?