Active directory Users and Computers delete old computer accounts automatically

we have a 2008 forest/domain structure, when we have computer accounts that are removed from the domain by unplugging them and not properly disjoining them from the domain it leaves a stale record of which appears to never be deleted. How can ADUC do this automatically instead of purging it manually. I'm running ADUC ver 6.1.7601.17514

Thanks,