Bunset
From Scriptwiki
The bunset command is used to unset a binary file.
bunset <&binvar> [&binvar &binvar ... &binvar]
This unsets all specified binary files. Unlike unset, bunset doesn't work with wildcards.
Examples
bset &test 1 65 echo -a $bvar(&test,0) bunset &test echo -a $bvar(&test,0)
In this case the first echo will echo "1" as &test is filled with 1 byte, the second echo will echo "0" as &test is unset.