Comment 2 for bug 1658147

Nevermind, ignore comment #1. I mis-read the question. I think you're trying to disable the new user in domain foo.

Trouble is, there is no option to specify a domain where the user exist.

# openstack user set --help

positional arguments:
  <user> User to modify (name or ID)

optional arguments:
  -h, --help show this help message and exit
  --name <name> Set user name
  --project <project> Set default project (name or ID)
  --project-domain <project-domain>
                        Domain the project belongs to (name or ID). This can
                        be used in case collisions between project names
                        exist.
  --password <password>
                        Set user password
  --password-prompt Prompt interactively for password
  --email <email-address>
                        Set user email address
  --description <description>
                        Set user description
  --enable Enable user (default)
  --disable Disable user

There should be a --domain option in there to specify the user's domain that you are modifying.