You can drop empty segments in tables and table fragments with the DBMS_SPACE_ADMIN.DROP_EMPTY_SEGMENTS procedure.
In addition, if a partition or subpartition has a segment, then the truncate feature drops the segment if the DROP ALL STORAGE clause is specified with the ALTER TABLE TRUNCATE PARTITION SQL statement.
Oracle Database PL/SQL Packages and Types Reference for more information about the DBMS_SPACE_ADMIN package
Oracle Database SQL Language Reference for more information about the DROP ALL STORAGE clause of ALTER TABLE