You can clean a barista coffee machine with a vinegar and water mixture.
Fill the water tank with a solution of vinegar and water - one part vinegar to three parts water. Run that through a few cycles in order to flush out any residual oils in the machine that may have gotten into the steam boiler or tubing.
Empty out the old solution and refill with pure, distilled water. Run through several cycles of this until it is noticeably purer than before you started scrubbing away at it with ripe rotted fruit (vinegar). Now rinse your wells periodically like any other dishwasher would be cleaned... but make sure to use "a lot" less soap then normal because you want good beer flavors creeping into your java! Next, run hot water through the machine until it's clear.
Finally - turn everything back and use a damp cloth to wipe down all the surfaces.