Question:
What is the parameter to blacklist the domain(s) to be excluded from the trusts?

Answer:
Before Centrify DirectControl 5.1.2, 'adclient.ldap.trust.excluded.domains' is used to blacklist unwanted domains. 

• Edit /etc/centrifydc/centrifydc.conf and add the following parameter to the bottom of the file​​

Starting from Centrify DirectControl 5.1.2, new parameter 'adclient.excluded.domains' is introduced.

• Edit /etc/centrifydc/centrifydc.conf and add the following parameter to the bottom of the file​​

(https://www.centrify.com/downloads/products/documentation/suite2013/2013.3-release-notes/DirectControl-Release-Notes.html)

Please replace the <domain> with unwanted domain name and separate the names with white space. 

Please run the following commands as root to make the changes in configuration file effective:

# adreload
# adflush