VMS Help DEASSIGN, Qualifiers, /JOB  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Indicates that the specified logical name is in the jobwide
    logical name table. The /JOB qualifier is synonymous with the
    /TABLE=LNM$JOB qualifier. If you do not explicitly specify a
    logical name table, the default is the /PROCESS qualifier.

    You should not deassign jobwide logical name entries that were
    made by the system at login time, for example, SYS$LOGIN,
    SYS$LOGIN_DEVICE, and SYS$SCRATCH. However, if you assign new
    equivalence names for these logical names (that is, create new
    logical names in outer access modes), you can deassign the names
    you explicitly created.