def unsetDomainOnDeactivation(domain, event):
    """Unset the permission id up registration deactivation.

    Let's see how this notifier can be used. First we need to create an event
    using the permission instance and a registration stub:

    >>> class Registration:
    ...     def __init__(self, obj, name):
    ...         self.component = obj
    ...         self.name = name

    >>> domain1 = TranslationDomain()
    >>> domain1.domain = 'domain1'

    >>> import zope.interface.interfaces
    >>> event = zope.interface.interfaces.Unregistered(
    ...     Registration(domain1, 'domain1'))

    Now we pass the event into this function, and the id of the role should be
    set to '<domain not activated>'.

    >>> unsetDomainOnDeactivation(domain1, event)
    >>> domain1.domain
    '<domain not activated>'
    """
    domain.domain = '<domain not activated>'
