All the user documentation for scrub is in the scrub(1) manual page. To format the manual page from the source directory, run something like:

nroff -man scrub.1 | less

On testing with the 'make check' target: Set TMPDIR to a file system that allows you to create a >4GB sparse file. On an AIX JFS file system, the file system must have been created with large file support. Also, ensure that your file size ulimit is set to unlimited.