Once you create display campaign and save it to create ad strategies, under the targeting options you can define the Black list domains.
You can define templates for website domains, lists of terms within website URLs, and user zip codes or postal codes within a single country to exclude as targets for any of your managed display ad strategies. You can also create blacklist templates, and define individual domains, URL terms, and zip codes and postal codes to exclude as targets, within individual RTB ad strategies. Blacklists always override whitelists. If your settings both exclude and include the same target for an ad, the target is excluded.
Here are the steps to create a website blacklist:
In the main menu, click Display > Tools & Settings > Blacklists / Whitelists.
Choose the type of template to create:
To create a template of domains to exclude, click Blacklist Domains.
To create a template of URL terms to exclude, click Blacklist URL Terms.
To create a template of zip codes or postal codes to exclude, click Blacklist Zip Codes.
Enter the list name.
In the input field, enter information about the targets to exclude, each on a separate line.
(Blacklisted domains) Enter each website to exclude, each on a separate line.
URLs must be valid and can include up to three domain levels (for example, my.example.com but not my.new.example.com) and two path levels (for example, example.com/news/local but not example.com/news/local/sports).
(Blacklisted URL terms) Enter each term within URLs to exclude, each on a separate line.
Each term can occur between certain special characters (such as periods in the domain name and forward slashes) and is ignored if it occurs after a "?" symbol. For example, if the blacklist included the term "games," you won't bid on the site example.com/products/games?myparam=graphics.
(Blacklisted zip codes) To enter zip codes or postal codes to exclude for a single country, do the following:
Select the country.
Enter each user zip code or postal to exclude, each on a separate line.
(Optional) To automatically select the template for all new ad strategies, select Automatically apply this template to new ad strategies.
I hope this helps.