/sys$common/syshlp/helplib.hlb SCA, SET, NOLIBRARY, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 library-spec[, . . . ]
    Specifies the libraries to be removed from the current active
    libraries list. If you omit this parameter, SCA removes all the
    active libraries from the list.