yes, blocking an email domain across all forms is really time consuming.
There are 2 steps.
First; you need to excule domain name from the form and update it.
Second; you will need to see that on how many website pages; the form appears. You will then have to go to each website page and update the website page; so the form is update on that website page.
This process is really long and I wish that hubspot provides any workflow or any option to update the forms on all website pages in one click.