You would like to set up Deny permissions for a specific set of users in a User Group over a Space so that anyone but the users in this User Group can access the Space.
While setting up Deny permissions in such a manner is currently not possible in the product, a feature enhancement request for a future product release has been raised with issue key JIVESPECS-1484.
You can bookmark the Jive Cloud Release Schedule page on Worx to track the release of this enhancement request. Please note that enhancement requests take time to implement and they are also subject to approval, therefore there is no guarantee that they will be actually included in a specific future release.
If you don't have access to Worx, you can request an account.
Alternatively, you can choose to only assign the access permissions for the users/user groups that should have access to the Space. This will ensure that anyone who hasn't been added, will not be able to access the Space.
Or, you can set up user overrides for the individual users (not user groups) that should be denied access to the Space.