Resolution
SSO logout-url is stored in database of SSO server /var/lib/sso/sso.db. It is configured during registration of Parallels Plesk Panel in SSO server to match Plesk full hostname. Plesk full hostname is stored in table misc of Plesk database.
It may be viewed and configured through Parallels Plesk Panel interface and in Plesk database directly.
In Parallels Plesk Panel GUI {Settings -> Server Settings -> Full hostname}. Use the following command to check the parameter in Plesk database:
~# mysql -uadmin -p`cat /etc/psa/.psa.shadow` psa -e"select * from misc where param='FullHostName'"
+--------------+----------------+
| param | val |
+--------------+--------------- +
| FullHostName | <old hostname> |
+--------------+----------------+
~#