Ghost user unit

I have a problem with ghost user units. The accounts were defined using pam through ldap, with the creation of a home directory.

If I delete the account in LDAP, there remains a corresponding user unit, with warning during a nixos-rebuilt such as

reloading user units for johndoe...
No passwd entry for user 'johndoe'

This means that there remains some traces of johndoe, but I cannot find where.

What can I do to get rid of this?