Recent observations have revealed that at least eight globular clusters (GCs) in the Galaxy show internal abundance spreads in [Fe/H]. We investigate the origin of these "anomalous" GCs using numerical simulations of GCs in the dwarfs orbiting around the Galaxy and chemical evolution model of the dwarfs hosting the GCs. The principal results are as follows. GCs formed in a host dwarf galaxy with a total mass of ∼1010 M⊙can merge to form a single nuclear GC before the host is completely destroyed by the Galaxy, if they are massive (∼ 3 × 105 M⊙) and if they are formed in the inner region (R < 400pc). The GC merger remnants can capture field stars during its spiral-in to nuclear regions. If two GCs are formed from star formation events separated by ∼300 Myr in their host dwarf, then the new GC formed from GC merging can have a [Fe/H] spread of 0.2 dex and a [Ba/Fe] spread of 0.3 dex. GCs formed from GC merging can show a variety of internal abundance spreads depending on the details of their hosts' chemical evolution. We suggest that anomalous GCs were formed from GC merging that occurred before the destruction of GC host dwarfs, yet after self-enrichment processes responsible for the observed anti-correlations between chemical abundances of light elements. We also suggest that the observed no/little dependence of [Eu/Fe] on [Fe/H] in the Galactic GC M22 is evidence of massive dwarf galaxies hosting these anomalous GCs.