To remove a particular item from Search Index, we can go to SSA (Search Service Administration) in CA (Central Administration) and click on Crawl log and URL view, then Remove the item from Index is possible.
Is there anyway, where we can use PowerShell/Code to perform the same task?
Could not find the answer here in as well Similar Question
References: Technet Link
Edit: Resetting the index is a no-go, also I don't want to exclude them via query rules in the results web part.
I assume that if I can delete them one by one in CA that there is a method to feed a couple of thousands at once to it to delete.
Checked here , https://www.reddit.com/r/sharepoint/comments/3skyzg/delete_items_from_index/ --> But that code is not working for me, any ideas?