I made this tool specifically for SEO. TO be able to identify unique referring domains. If you have a list of domains here, you can paste it in the first input field.
It will then give you an output of unique domains along with how many duplicates were found. You can now grab a second list of domains and check against the first list.
You will get a second output. You can copy the second output if you want to build links with. The 3rd output combines everything.