Simple Applescript that can be run from the command line to programmatically reset the iOS simulator.

reset_simulator.applescript

tell application "iPhone Simulator"
    activate
end tell

tell application "System Events"
    tell process "iPhone Simulator"
        tell menu bar 1
            tell menu bar item "iOS Simulator"
                tell menu "iOS Simulator"
                    click menu item "Reset Content and Settings…"
                end tell
            end tell
        end tell

        tell window 1
            click button "Reset"
        end tell
    end tell
end tell

-- Run at the command line or from a shell script using something like: 'osascript reset_simulator.applescript'

In Mavericks, it was not finding the Reset button. I changed the line to "click button 1" and it worked.

+1 RussVanBert's comment

In Yosemite + iOS Simulator 8.3, I changed the string of "iPhone Simulator" to "iOS Simulator" and it worked.

Updated for El Capitan (10.11.4), Xcode Version 7.3.1, iOS Simulator Version 9.3

tell application "Simulator"
    activate
end tell

tell application "System Events"
    tell process "Simulator"
        tell menu bar 1
            tell menu bar item "Simulator"
                tell menu "Simulator"
                    click menu item "Reset Content and Settings…"
                end tell
            end tell
        end tell
        tell window 1
            click button "Reset"
        end tell
    end tell
end tell