Everybody, thanks for your help and advice but the old-timer's advice to go the d ^%GOF route in Cache Terminal proved to be it. It was actually amazing to see how much superior this route turned out to be comparing with the much more modern Export/Import Management Portal route. Specifically:

  1. Preparation to exclude certain globals, few dozens of them: Terminal - about 10 minutes because you can use ranges (see below and here, https://docs.intersystems.com/priordocexcerpts/prgglobalchui-41.pdf), portal - much longer because you have to uncheck each global individually
  2. Export speed: Terminal - 10 minutes, portal 3 hours (no kidding)
  3. Export/Import log per global: Terminal - log provided, complete with the number of blocks per global, portal - no log
  4. Import speed: Terminal - less than 10 minutes, portal - stuck in the middle with no error shown

Sample %GOF usage in terminal, hit Enter if no special requests, exporting:
d ^%GOF
Device: tmp.gof
           file format: ("UNW*") =>
          Maximum media size (bytes): (No maximum)
Enter a short description of the contents of this tape or file
All Globals? No => No
Global ^S-SZ         [All globals in this range, case-sensitive - AG]
Global ^'STPL*     [Exclude all globals that start with STPL - AG]

Real life output from my real life usage:
^ZPG                                           182 data blocks written
^ZTEMP                                           1 data block written
491,337 blocks written in 10 minutes,  51 seconds
Importing was done via d ^%GIF, via terminal as well. At some point the %GIF utility asked me:

Globals with a preceding asterisk ('*') already exist in this directory
What would you like to do with these globals that exist?
1. Skip inputting globals that exist in this directory
2. Merge input globals with the existing globals
3. Specify skip/merge for individual globals
Your choice: 1=>

Thanks again,

Apparently GBLOCKCOPY is simply not available on my Cache 2017 version since search for it in system files returns nothing. I am trying to transfer a large number of globals, not all, from one computer to another, not just between namespaces within the same database. The system does not have actively modified globals. I got an old-timer advice to use %GOF which does accept ranges both for exclusion and inclusion so will work on that for a while.

It looks like  code below would give me what I am looking for. Just need to figure out (or take an advice!) how to exclude, say, system classes outright. 

f  {
x=rs.Next() q:'x
P.S. Found the answer to my last question: https://cedocs.intersystems.com/latest/csp/documatic/%25CSP.Documatic.cls?PAGE=CLASS&LIBRARY=%25SYS&CLASSNAME=%25Library.RemoteResultSet