multiple independent simulations

[Berezovsky]

I would like to create independent, concurrent simulations in memory and have them all operate independently without fear of global data cross-talk. I have discovered recently that this is far more difficult than merely declaring independent classes. Even cleaning up previous instantiations leaves traces around that interfere with the new ones. I would appreciate any tutorials that go in this direction or any links which address how various simulations might interfere with each other, even though they appear as independent classes. Thank you.