[CentOS] yum tries to install a mix of architectures

Hello,

 On my centos boxes whenever I try to install packages I get a mix of
packages from the repos that are both i386 and x86_64 in
archictecture:

===============================================================================================================================================================================================================
 Package                                             Arch
                             Version
              Repository                                    Size
===============================================================================================================================================================================================================
Installing:
 boost-devel                                         i386
                             1.33.1-10.el5
              base                                         4.3 M
 boost-devel                                         x86_64
                             1.33.1-10.el5
              base                                         4.4 M
Installing for dependencies:
 boost                                               i386
                             1.33.1-10.el5
              base                                         863 k
 boost                                               x86_64
                             1.33.1-10.el5
              base                                         861 k
 libicu                                              i386
                             3.6-5.11.4
              base                                         5.2 M
 libicu                                              x86_64
                             3.6-5.11.4
              base                                         5.2 M

Transaction Summary
===============================================================================================================================================================================================================
Install       6 Package(s)
Upgrade       0 Package(s)




Without having so specify the arch on each yum command how can I
automatically prune my yum repo files so that it will only grab
packages that relate to the architecture I'm running?


Thanks in advance!


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