When using an RPM based Linux distribution, you have to put RPM Search
in your Bookmarks. This search tool will produce all available RPM files available on planet Earth.
Scientific Linux is based on Red Hat Enterprise Linux. If you do an advanced search at RPM search using "libstdc++.so.6.0.9" as key words in the search field and checking all RHEL entries plus 'Other' in the "Other" section, you'll find there is no package that has this library for RHEL.
But if you do an advanced search and hit the "Check All" switch using 'libstdc++.so.6.0.9' as keywords, you'll find this library is available for Mandriva, Suse, Open Suse, and Ark Linux.
What this tell me....is that you cannot install the new version of Skype on Scientific Linux using a .rpm file, you'll have to look for a source package.
That's just the way my deductive reasoning skills deduce your predicament, perhaps the deductive reasoning skills of others may quash my deductive reasoning skills.