How to secure the hybrid cloud

Increasingly, the cloud is becoming mixed up; and that's not a bad thing. Enterprises of all sizes are starting to conclude that more often than not a mixture of public and private cloud solutions provide the best operating efficiencies and value proposition. This is, in a nutshell, the hybrid cloud. Wikipedia defines it rather well as being "a composition of two or more clouds that remain distinct entities but are bound together, offering the benefits of multiple deployment models" and you can explore the concept further through some interesting Cloud Pro case studies. Time and time again you will find yourself being advised to audit your data and applications, keeping the highest risk stuff within a private cloud environment while farming the lower risk functions and data out into the public cloud. It's good enough advice. Indeed, I have often given it myself, but the question is raises which is not so often answered is how do you then ensure that this overall hybrid cloud entity is secure?