How To Transfer a Google Doc to a User with a Different Domain

Google does not allow the transfer of ownership of your Google doc, Google sheet, or Google form to a user with a different domain.

Example: user@brodneil.com cannot transfer ownership to user@gmail.com because brodneil.com and gmail.com are two different domains.

Here is a workaround and hopefully it will still be working by the time you are reading this post:

Share your file (Google doc, Google sheet, or Google form) to the intended user with Edit capabilities or as Editor.
Ex. user@brodneil.com shares a file called file1 to user@gmail.com.
Ask that user to copy the file you shared in Google drive as a different file.
Ex. user@gmail.com opens Google Drive and copies file1. And thus you will have two copies after, file1 and copy of file1, in Google drive after.
Rename the copied file (optional)
Ex. copy of file1 is renamed to file2.
Open file2 and check the ownership under settings.
Ex. Owner of file1 is user@brodneil.com, but the owner of the copied file, file2, is user@gmail.com
You can share the new (copied) file to the previous owner if you still want to give that user an editing or viewing access(optional)
Ex. Share file2 to the previous owner, user@brodneil.com.

The outcome would then be: