Hi! Can you clarify your question a little bit please? You said "dropped domain." What do you mean by that? It sounds like what I'm hearing you say is that you had an old domain that was dropped from Google, but you are concerned that actual visitors to that old domain are able to find your new domain, without inheriting the bad link profile that may ahve cause the old domain to get dropped.
Honestly, you may not be able to accomplish what you are wanting. But I need to know more first so that's why I asked for clarification. I'd be glad to help if possible.
Cheers,
Dana

You're awesome. This is a perfect example why Moz Q & A rocks