Automator workflow / app to refresh a given tab in Safari (or even Crome)
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