Paste this script into script editor and save it as a service. Map the service to a keyboard shortcut.
tell application "Safari"
activate
tell current tab of window 1
do JavaScript "location.reload();"
end tell
end tell
EDIT
tell application "Safari"
activate
tell window 1
--options
set myTab to tab 1
set myTab to first tab whose URL = "https://apple.stackexchange.com/questions/224393/automator-workflow-app-to-refresh-a-given-tab-in-safari-or-even-crome/224431?noredirect=1#comment272178_224431"
set myTab to first tab whose URL starts with "https://apple.stackexchange.com"
if current tab is not myTab then set current tab to myTab
tell myTab to do JavaScript "location.reload();"
end tell
end tell
EDIT 2
Select your tab and run this script to get its name
tell application "Safari"
activate
tell window 1
get name of current tab
end tell
end tell
Populate the name in this script:
tell application "Safari"
activate
tell window 1
set myTab to first tab whose name = "insert name here"
if current tab is not myTab then set current tab to myTab
tell myTab to do JavaScript "location.reload();"
end tell
end tell