IT had written a script to return a list of domains in your Cloud organization.

If you want to ensure that the script can no longer access the information about the domains in your Cloud organization, you need to revoke the API key that was used to authenticate the script. An API key is a token that allows you to manage your organization via the admin APIs1. You can create, view, and revoke API keys from the organization settings2. Revoking an API key will invalidate it and prevent any further requests using that key2.

The other options are not relevant or effective for stopping the script from accessing the information. Removing DNS records or removing a verified domain will not affect the API key that was used by the script. It will only affect the verification status of your domain and the management of your users and accounts3. Regenerating a security key will not affect the API key that was used by the script. It will only affect the encryption of your data at rest4. Deleting an IP allowlist will not affect the API key that was used by the script. It will only affect the IP addresses that are allowed to access your organization and products5.

References :

Manage an organization with the admin APIs

Create and revoke API keys

Verify a domain to manage accounts

Regenerate your security key

Set up an IP allowlist