https://access.stage.redhat.com/documentation/en/red-hat-jboss-enterprise-application-platform/version-7.0.beta/management-cli-guide/#management_cli_command_history
Current content:

Clear the Management CLI Command History

Clear the history of CLI commands from the session memory. The CLI command history is still present in the .jboss-cli-history file saved to the user's home directory.

jboss-cli behaves as following:
Once user initialize a CLI session, the history is loaded to memory from the .jboss-cli-history file. Until the user ends the session, only in-memory history is used, CLI doesn't touch the history file during the session, the file is updated when user terminates the session.

Invoking the history --clear may look like the history file remain untouched, but once user terminates the session the file will be overwritten by a history from memory.

Alexey is taking care of the operation description in JBEAP-3184