Unfortunately, you have to do it one by one. This can be a daunting task if you are an old member with hundreds of open sales threads.
Fortunately, moderators such as myself can indiscriminately close all threads in a matter of seconds (minutes) though. It wouldn't be my first time doing so, and probably not my last either, but I am here to help and serve our community members.
Would you like me to close all of your sales threads for you?
You can then start fresh. Later on, you can go back and edit out the domains in the title and contents of the threads if you wish too. This, I cannot do as it'd bury me in work.