Here are a couple of methods to remove all the CI data from the CMDB and keep all other items like correlation rules, TQLs, reports, maps, etc.
The following methods are advisable, where the first one is the preferred one.
1) To delete CI's using the JMX console on the DPS server, go to service=CMDB Model Services under Topaz, then use the java.lang.String deleteByClassType() mBean.
2) If you are trying to clear all data out of the CMDB, and everything else in the CMDB is out of the box, then you may try just connecting to a new CMDB, which can be done by stopping BAC and running the connect to database utility. Connect to existing databases for management and create new CMDB and CMDB history databases.
3) You can also use Enrichment rules to remove CI instances. In this case, I would need to contact a CMDB support engineer for help on this.