I was ghosted on mainland recently and had a friendly soul help me sort it out.
First off she pointed me to:
http://blogs.secondlife.com/message/424221#424221Which includes the standard ghosting options (have owner or LL reset sim) but also a do-it-yourself option that actually worked for me to un-ghost my AV (the bottom of the second message in the thread describes the procedure).
She also pointed me to a JIRA ticket to request LL create an Avatar Reset option, though it may be technically impossible, voting on it would help highlight the issue.
Another tidbit I gleaned from this is it is likely scripted objects crossing sim lines are the cause of the ghosting. Of course vehicles are one but also consider clothing with resizing scripts and other worn items with scrips in them, the less of those you are wearing when traversing sims the better chance of a successful crossing.
For her help she requested I pass it on to others in need, so there ya go, hope it doesnt happen to you, but now at least we have something to try instead of waiting for for a sim reset.