If I understand your question, all you should have to do is delete all the inventories. You can do it manually or just set the Days to Keep Inventory Scans to a low number under the Inventory tab of settings and get rid of anything older than X days.
Yeah - selecting "all the devices" in the console view & hitting delete will do that job but ... that's a really bad idea, I'd argue.
For one, you don't want to delete the Core server entry itself (that may still cause some weird nonsense to happen, as the Core may not know of itself in that situation).
What ACTUAL problem are you trying to address / solve here? Letting us know THAT may be more useful as we can give you better advice potentially.